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  <div class="head">
   <p data-fill-with="logo"><a class="logo" href="https://www.w3.org/"> <img alt="W3C" height="48" src="https://www.w3.org/StyleSheets/TR/2016/logos/W3C" width="72"> </a> </p>
   <h1 class="p-name no-ref" id="title">CSS Foo Module Level 1</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Editor’s Draft, <time class="dt-updated" datetime="1970-01-01">1 January 1970</time></span></h2>
   <details>
    <summary>Specification Metadata</summary>
    <div data-fill-with="spec-metadata">
     <dl>
      <dt>This version:
      <dd><a class="u-url" href="https://drafts.csswg.org/css-foo/">https://drafts.csswg.org/css-foo/</a>
      <dt>Latest published version:
      <dd><a href="https://www.w3.org/TR/css-foo/">https://www.w3.org/TR/css-foo/</a>
      <dt class="editor">Editors:
      <dd class="editor p-author h-card vcard"><a class="p-name fn u-url url" href="http://example.com/contact">Name1</a> (<span class="p-org org">Company1</span>)
      <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:name2@example.com">Name2</a> (<span class="p-org org">Company2</span>)
      <dt>Suggest an Edit for this Spec:
      <dd><a href="https://github.com/w3c/csswg-drafts/blob/master/css-foo-1/Overview.bs">GitHub Editor</a>
      <dt>Issue Tracking:
      <dd><a href="https://github.com/w3c/csswg-drafts/labels/css-foo-1">GitHub Issues</a>
     </dl>
    </div>
   </details>
   <div data-fill-with="warning"></div>
   <p class="copyright" data-fill-with="copyright"><a href="https://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 1970 <a href="https://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a href="https://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href="https://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href="https://www.keio.ac.jp/">Keio</a>, <a href="https://ev.buaa.edu.cn/">Beihang</a>). W3C <a href="https://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a href="https://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and <a href="https://www.w3.org/Consortium/Legal/2015/copyright-software-and-document">permissive document license</a> rules apply. </p>
   <hr title="Separator for header">
  </div>
  <div class="p-summary" data-fill-with="abstract">
   <h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
   <p>This module introduces the <a class="property" data-link-type="propdesc" href="#propdef-foo" id="ref-for-propdef-foo">foo</a> property and related values, which do bar and baz.</p>
    <a href="https://www.w3.org/TR/CSS/">CSS</a> is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, etc. 
  </div>
  <h2 class="no-num no-toc no-ref heading settled" id="status"><span class="content">Status of this document</span></h2>
  <div data-fill-with="status">
   <p> This is a public copy of the editors’ draft.
	It is provided for discussion only and may change at any moment.
	Its publication here does not imply endorsement of its contents by W3C.
	Don’t cite this document other than as work in progress. </p>
   <p> <a href="https://github.com/w3c/csswg-drafts/issues">GitHub Issues</a> are preferred for discussion of this specification.
	When filing an issue, please put the text “css-foo” in the title,
	preferably like this:
	“[css-foo] <i data-lt>…summary of comment…</i>”.
	All issues and comments are <a href="https://lists.w3.org/Archives/Public/public-css-archive/">archived</a>,
	and there is also a <a href="https://lists.w3.org/Archives/Public/www-style/">historical archive</a>. </p>
   <p> This document was produced by the <a href="https://www.w3.org/Style/CSS/">CSS Working Group</a>. </p>
   <p> This document was produced by a group operating under
	the <a href="https://www.w3.org/Consortium/Patent-Policy/">W3C Patent Policy</a>.
	W3C maintains a <a href="https://www.w3.org/2004/01/pp-impl/32061/status" rel="disclosure">public list of any patent disclosures</a> made in connection with the deliverables of the group;
	that page also includes instructions for disclosing a patent.
	An individual who has actual knowledge of a patent which the individual believes contains <a href="https://www.w3.org/Consortium/Patent-Policy/#def-essential">Essential Claim(s)</a> must disclose the information in accordance with <a href="https://www.w3.org/Consortium/Patent-Policy/#sec-Disclosure">section 6 of the W3C Patent Policy</a>. </p>
   <p> This document is governed by the <a href="https://www.w3.org/2019/Process-20190301/" id="w3c_process_revision">1 March 2019 W3C Process Document</a>. </p>
   <p></p>
  </div>
  <div data-fill-with="at-risk"></div>
  <nav data-fill-with="table-of-contents" id="toc">
   <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
   <ol class="toc" role="directory">
    <li><a href="#intro"><span class="secno">1</span> <span class="content">Introduction</span></a>
    <li>
     <a href="#sample-topic"><span class="secno">2</span> <span class="content">Sample section</span></a>
     <ol class="toc">
      <li><a href="#the-foo-property"><span class="secno">2.1</span> <span class="content">Internal display model: the <span class="property">foo</span> property</span></a>
      <li><a href="#shorthands"><span class="secno">2.2</span> <span class="content">Shorthands and Descriptors</span></a>
     </ol>
    <li><a href="#priv-sec"><span class="secno"></span> <span class="content">Privacy and Security Considerations</span></a>
    <li>
     <a href="#conformance"><span class="secno"></span> <span class="content"> Conformance</span></a>
     <ol class="toc">
      <li><a href="#document-conventions"><span class="secno"></span> <span class="content"> Document conventions</span></a>
      <li><a href="#conform-classes"><span class="secno"></span> <span class="content"> Conformance classes</span></a>
      <li>
       <a href="#conform-responsible"><span class="secno"></span> <span class="content"> Requirements for Responsible Implementation of CSS</span></a>
       <ol class="toc">
        <li><a href="#conform-partial"><span class="secno"></span> <span class="content"> Partial Implementations</span></a>
        <li><a href="#conform-future-proofing"><span class="secno"></span> <span class="content"> Implementations of Unstable and Proprietary Features</span></a>
        <li><a href="#conform-testing"><span class="secno"></span> <span class="content"> Implementations of CR-level Features</span></a>
       </ol>
     </ol>
    <li>
     <a href="#index"><span class="secno"></span> <span class="content">Index</span></a>
     <ol class="toc">
      <li><a href="#index-defined-here"><span class="secno"></span> <span class="content">Terms defined by this specification</span></a>
      <li><a href="#index-defined-elsewhere"><span class="secno"></span> <span class="content">Terms defined by reference</span></a>
     </ol>
    <li>
     <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
     <ol class="toc">
      <li><a href="#normative"><span class="secno"></span> <span class="content">Normative References</span></a>
     </ol>
    <li>
     <a href="#property-index"><span class="secno"></span> <span class="content">Property Index</span></a>
     <ol class="toc">
      <li><a href="#some-at-rule-descriptor-table"><span class="secno"></span> <span class="content"><span>@some-at-rule</span> Descriptors</span></a>
     </ol>
    <li><a href="#idl-index"><span class="secno"></span> <span class="content">IDL Index</span></a>
    <li><a href="#issues-index"><span class="secno"></span> <span class="content">Issues Index</span></a>
   </ol>
  </nav>
  <main>
   <h2 class="heading settled" data-level="1" id="intro"><span class="secno">1. </span><span class="content">Introduction</span><a class="self-link" href="#intro"></a></h2>
   <p><em>This section is not normative.</em></p>
   <p>Due to the need to have example specifications,
	the CSS community found a great need to have a <a class="property" data-link-type="propdesc" href="#propdef-foo" id="ref-for-propdef-foo①">foo</a> property.
	This specifications addresses this need in
	a very simply way.
	While it provides a very limited set of features for authors,
	it effectively demonstrates how to write a CSS specification.</p>
   <h2 class="heading settled" data-level="2" id="sample-topic"><span class="secno">2. </span><span class="content">Sample section</span><a class="self-link" href="#sample-topic"></a></h2>
   <p>Look at the mark-up in this section for examples.
	See the <a href="https://github.com/tabatkins/bikeshed/blob/master/README.md">documentation</a> for more precise instructions.
	The companion of this template shows the <a href="Overview.html">processed result</a>.</p>
   <p>To refer to HTML, use <a data-link-type="biblio" href="#biblio-html">[HTML]</a> (note the double square brackets in the source).
	To make a normative reference,
	insert a “!”, like this: <a data-link-type="biblio" href="#biblio-css-syntax-3">[CSS-SYNTAX-3]</a> The currently available <a href="https://www.w3.org/Style/Group/css3-src/biblio.ref">list of bibliographic data</a> can of course be extended.</p>
   <p>We write about a property such as <a class="property" data-link-type="propdesc" href="#propdef-foo" id="ref-for-propdef-foo②">foo</a> like this
	and about a piece of CSS code like this: <span class="css" id="ref-for-propdef-foo③">foo: bar</span>.
	(Note that if it looks like a "property: value",
	it’ll automatically link to the property.)
	Inline HTML and XML are similar,
	but use the CODE element: <code class="lang-html highlight"><c- p>&lt;</c-><c- f>blockquote</c-><c- p>></c->...<c- p>&lt;/</c-><c- f>blockquote</c-><c- p>></c-></code> and <code class="lang-xml highlight"><c- f>&lt;r:xyz></c->...<c- f>&lt;/r:xyz></c-></code>.</p>
   <p class="note" role="note"><span>Note:</span> Note that the property will automatically be linked to its definition.</p>
   <p>To define <dfn data-dfn-type="dfn" data-export id="terms">terms<a class="self-link" href="#terms"></a></dfn> into the <dfn data-dfn-type="dfn" data-export id="dfn-index">index<a class="self-link" href="#dfn-index"></a></dfn>,
	there are many <dfn data-dfn-type="dfn" data-export data-lt="variant" id="variant">variants<a class="self-link" href="#variant"></a></dfn>,
	but hopefully the <dfn data-dfn-type="dfn" data-export id="simplest" title="simple|simpler|simplest">simplest<a class="self-link" href="#simplest"></a></dfn> will be the most common.
	Note that you need to explicitly export any plain <code><a data-link-type="element" href="https://html.spec.whatwg.org/multipage/text-level-semantics.html#the-dfn-element" id="ref-for-the-dfn-element">dfn</a></code>s you want to be linkable from other specs,
	but all other types of definition automatically export themselves.</p>
   <p class="note" role="note"><span>Note:</span> Note that you can add non-normative notes like this.</p>
   <p>Of course, multi-paragraph notes are also possible: just enclose them in a <code><a data-link-type="element" href="https://html.spec.whatwg.org/multipage/grouping-content.html#the-div-element" id="ref-for-the-div-element">div</a></code>:</p>
   <div class="note" role="note">
     Note that this note is a multi-paragraph note. 
    <p>It doesn’t <em>need</em> to have two paragraphs, but it could.</p>
   </div>
   <details class="note">
    <summary>A longer note</summary>
    <p>When you want to insert a longer note
		to provide some useful explanation,
		but the note itself is not critical to the section it’s placed in,
		use a <code><a data-link-type="element" href="https://html.spec.whatwg.org/multipage/interactive-elements.html#the-details-element" id="ref-for-the-details-element">details</a></code> note instead.</p>
    <p>This will hide the note by default,
		so it’s less distracting to the flow of the section.
		(At least, in browsers that support <code><a data-link-type="element" href="https://html.spec.whatwg.org/multipage/interactive-elements.html#the-details-element" id="ref-for-the-details-element①">details</a></code>;
		legacy browsers will get something like a normal note.)</p>
   </details>
   <p>Displayed examples come in eight different types:
	CSS examples that need no separate paragraph of explanation are put in a simple PRE:</p>
<pre class="example lang-css highlight" id="example-f8c184cb"><a class="self-link" href="#example-f8c184cb"></a><c- f>EM </c-><c- p>{</c-> <c- k>font-style</c-><c- p>:</c-> italic <c- p>}</c->
</pre>
   <p>CSS examples that need extra text need a DIV.</p>
   <div class="example" id="example-37ecc6e5">
    <a class="self-link" href="#example-37ecc6e5"></a> The following example is the same as the previous one,
		but now it is explained: 
<pre class="lang-css highlight"><c- f>EM </c-><c- p>{</c-> <c- k>font-style</c-><c- p>:</c-> italic <c- p>}</c-></pre>
   </div>
   <p>Illegal CSS examples (examples of errors) are the same,
	but with class "illegal example".
	Examples of HTML and XML code have class "html" and "xml" respectively,
	but are otherwise ditto.</p>
   <p>A formal definition of a property looks like this:</p>
   <h3 class="heading settled" data-level="2.1" id="the-foo-property"><span class="secno">2.1. </span><span class="content">Internal display model: the <a class="property" data-link-type="propdesc" href="#propdef-foo" id="ref-for-propdef-foo④">foo</a> property</span><a class="self-link" href="#the-foo-property"></a></h3>
   <table class="def propdef" data-link-for-hint="foo">
    <tbody>
     <tr>
      <th>Name:
      <td><dfn class="dfn-paneled css" data-dfn-type="property" data-export id="propdef-foo">foo</dfn>
     <tr class="value">
      <th><a href="https://drafts.csswg.org/css-values/#value-defs">Value:</a>
      <td class="prod">inline-inside <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-4/#comb-one" id="ref-for-comb-one">|</a> block-inside <span id="ref-for-comb-one①">|</span> table <span id="ref-for-comb-one②">|</span> ruby <span id="ref-for-comb-one③">|</span> icon 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#initial-values">Initial:</a>
      <td>text 
     <tr>
      <th>Applies to:
      <td><a href="https://drafts.csswg.org/css-pseudo/#generated-content" title="Includes ::before and ::after pseudo-elements.">all elements</a> 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#inherited-property">Inherited:</a>
      <td>no 
     <tr>
      <th><a href="https://drafts.csswg.org/css-values/#percentages">Percentages:</a>
      <td>n/a 
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#computed">Computed value:</a>
      <td>specified value 
     <tr>
      <th>Canonical order:
      <td>per grammar 
     <tr>
      <th><a href="https://drafts.csswg.org/web-animations/#animation-type">Animatable:</a>
      <td>no 
   </table>
   <dl>
    <dt><dfn class="css" data-dfn-for="foo" data-dfn-type="value" data-export id="valdef-foo-value-name">value-name<a class="self-link" href="#valdef-foo-value-name"></a></dfn> 
    <dd> Define values using a <code><a data-link-type="element" href="https://html.spec.whatwg.org/multipage/grouping-content.html#the-dl-element" id="ref-for-the-dl-element">dl</a></code>.
			Note that the <code><a data-link-type="element" href="https://html.spec.whatwg.org/multipage/grouping-content.html#the-dl-element" id="ref-for-the-dl-element①">dl</a></code> wrapper
			specifies the default <code><a data-link-type="element" href="https://html.spec.whatwg.org/multipage/text-level-semantics.html#the-dfn-element" id="ref-for-the-dfn-element①">dfn</a></code> type and what property it’s for,
			so you don’t have to repeat that information in each individual definition. 
   </dl>
   <p><dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="cross-references">Cross-references</dfn> are created by enclosing a term or phrase in &lt;dfn>
	(like the word <a data-link-type="dfn" href="#cross-references" id="ref-for-cross-references">cross-references</a> earlier in this sentence).
	Then an &lt;a> without an <code>href=""</code> attribute
	with the same text content will automatically be linked.
	Both &lt;dfn>s and &lt;a>s are typed,
	which allows the same text to appear as different types of terms without a collision.
	The type can often be inferred,
	but sometimes it needs to be specified,
	like when you’re linking to a <code class="idl"><a data-link-type="idl" href="#foo" id="ref-for-foo">Foo</a></code> WebIDL interface.
	(Here, we’re using the <em>IDL</em> linking shorthand
	to make it clear that this is one of the IDL types.)</p>
   <p>And a figure with a caption is done like this:</p>
   <figure>
     <img alt="A table with a caption above it; both have margins and the margins between them are collapsed, as is normal for vertical margins." src="corner.png"> 
    <figcaption> Just a random image.
			Use SVG if you can.
			Otherwise, W3C prefers PNG over GIF (obviously, since PNG is a W3C Rec). </figcaption>
   </figure>
   <p>Don’t forget to write the alt.</p>
   <p class="issue" id="issue-7d79807a"><a class="self-link" href="#issue-7d79807a"></a> An open issue or editorial remark is OK in a WD,
	but they should be resolved/removed before the document goes to “CR”
	(Candidate Recommendation).
	Use <code class="lang-html highlight">class="issue"</code> on an element,
	or begin a paragraph with “Issue:”.</p>
   <p class="issue" id="issue-33d58da0"><a class="self-link" href="#issue-33d58da0"></a> Inline issues will be copied into an <a href="#issues-index">Issues Index</a> at the end of the document,
	for easy reference.</p>
<pre class="idl highlight def">/* Write WebIDL in a &lt;pre class="idl"> as plain text. */
<c- b>interface</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="interface" data-export id="foo"><code><c- g>Foo</c-></code></dfn> {
  <c- b>readonly</c-> <c- b>attribute</c-> <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring" id="ref-for-cssomstring"><c- n>CSSOMString</c-></a> <dfn class="idl-code" data-dfn-for="Foo" data-dfn-type="attribute" data-export data-readonly data-type="CSSOMString" id="dom-foo-bar"><code><c- g>bar</c-></code><a class="self-link" href="#dom-foo-bar"></a></dfn>;
  <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-boolean" id="ref-for-idl-boolean"><c- b>boolean</c-></a> <dfn class="idl-code" data-dfn-for="Foo" data-dfn-type="method" data-export data-lt="baz(Arg1, Arg2)" id="dom-foo-baz"><code><c- g>baz</c-></code><a class="self-link" href="#dom-foo-baz"></a></dfn>(<a class="n" data-link-type="idl-name" href="#dictdef-foodict" id="ref-for-dictdef-foodict"><c- n>FooDict</c-></a> <dfn class="idl-code" data-dfn-for="Foo/baz(Arg1, Arg2)" data-dfn-type="argument" data-export id="dom-foo-baz-arg1-arg2-arg1"><code><c- g>Arg1</c-></code><a class="self-link" href="#dom-foo-baz-arg1-arg2-arg1"></a></dfn>, (<a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring" id="ref-for-cssomstring①"><c- n>CSSOMString</c-></a> <c- b>or</c-> <a class="n" data-link-type="idl-name" href="#foo" id="ref-for-foo①"><c- n>Foo</c-></a>) <dfn class="idl-code" data-dfn-for="Foo/baz(Arg1, Arg2)" data-dfn-type="argument" data-export id="dom-foo-baz-arg1-arg2-arg2"><code><c- g>Arg2</c-></code><a class="self-link" href="#dom-foo-baz-arg1-arg2-arg2"></a></dfn>);
};

<c- b>dictionary</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="dictionary" data-export id="dictdef-foodict"><code><c- g>FooDict</c-></code></dfn> {
  <c- b>sequence</c->&lt;<a class="n" data-link-type="idl-name" href="#foo" id="ref-for-foo②"><c- n>Foo</c-></a>> <dfn class="idl-code" data-dfn-for="FooDict" data-dfn-type="dict-member" data-export data-type="sequence<Foo> " id="dom-foodict-foos"><code><c- g>foos</c-></code><a class="self-link" href="#dom-foodict-foos"></a></dfn>;
  <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-boolean" id="ref-for-idl-boolean①"><c- b>boolean</c-></a> <dfn class="idl-code" data-dfn-for="FooDict" data-dfn-type="dict-member" data-export data-type="boolean " id="dom-foodict-bar"><code><c- g>bar</c-></code><a class="self-link" href="#dom-foodict-bar"></a></dfn>;
  <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring" id="ref-for-cssomstring②"><c- n>CSSOMString</c-></a> <dfn class="idl-code" data-default="&quot;qux&quot;" data-dfn-for="FooDict" data-dfn-type="dict-member" data-export data-type="CSSOMString " id="dom-foodict-baz"><code><c- g>baz</c-></code><a class="self-link" href="#dom-foodict-baz"></a></dfn> = "qux";
};
</pre>
   <h3 class="heading settled" data-level="2.2" id="shorthands"><span class="secno">2.2. </span><span class="content">Shorthands and Descriptors</span><a class="self-link" href="#shorthands"></a></h3>
   <p>Shorthand properties have a smaller set of values to provide:</p>
   <table class="def propdef" data-link-for-hint="shorthand-foo">
    <tbody>
     <tr>
      <th>Name:
      <td><dfn class="css" data-dfn-type="property" data-export id="propdef-shorthand-foo">shorthand-foo<a class="self-link" href="#propdef-shorthand-foo"></a></dfn>
     <tr class="value">
      <th><a href="https://drafts.csswg.org/css-values/#value-defs">Value:</a>
      <td class="prod">foo <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-4/#comb-one" id="ref-for-comb-one④">|</a> bar <span id="ref-for-comb-one⑤">|</span> baz
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#initial-values">Initial:</a>
      <td>see individual properties
     <tr>
      <th>Applies to:
      <td>see individual properties
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#inherited-property">Inherited:</a>
      <td>see individual properties
     <tr>
      <th><a href="https://drafts.csswg.org/css-values/#percentages">Percentages:</a>
      <td>see individual properties
     <tr>
      <th><a href="https://drafts.csswg.org/css-cascade/#computed">Computed value:</a>
      <td>see individual properties
     <tr>
      <th><a href="https://drafts.csswg.org/web-animations/#animation-type">Animation type:</a>
      <td>see individual properties
     <tr>
      <th>Canonical order:
      <td>per grammar
   </table>
   <p>Adding new values to an existing property? Use a partial:</p>
   <table class="def propdef partial" data-link-for-hint="foo">
    <tbody>
     <tr>
      <th>Name:
      <td><a class="css" data-link-type="property" href="#propdef-foo" id="ref-for-propdef-foo⑤">foo</a>
     <tr class="value">
      <th><a href="https://drafts.csswg.org/css-values/#value-defs">New values:</a>
      <td class="prod">another-icon
   </table>
   <p>Or when defining a descriptor, use a descdef block (partials work here, too):</p>
   <table class="def descdef">
    <tbody>
     <tr>
      <th>Name:
      <td><dfn class="css" data-dfn-for="@some-at-rule" data-dfn-type="descriptor" data-export id="descdef-some-at-rule-descriptor-foo">descriptor-foo<a class="self-link" href="#descdef-some-at-rule-descriptor-foo"></a></dfn>
     <tr>
      <th>For:
      <td><a class="css" data-link-type="at-rule">@some-at-rule</a>
     <tr>
      <th>Value:
      <td class="prod">more <a data-link-type="grammar" href="https://drafts.csswg.org/css-values-4/#comb-one" id="ref-for-comb-one⑥">|</a> values
     <tr>
      <th>Initial:
      <td>values
   </table>
   <p>(A required descriptor can use `Initial: n/a.)</p>
   <h2 class="no-num heading settled" id="priv-sec"><span class="content">Privacy and Security Considerations</span><a class="self-link" href="#priv-sec"></a></h2>
   <p class="issue" id="issue-2202014f"><a class="self-link" href="#issue-2202014f"></a> Make some considerations about privacy and security.</p>
  </main>
  <h2 class="no-ref no-num heading settled" id="conformance"><span class="content"> Conformance</span><a class="self-link" href="#conformance"></a></h2>
  <h3 class="heading settled" id="document-conventions"><span class="content"> Document conventions</span><a class="self-link" href="#document-conventions"></a></h3>
  <p>Conformance requirements are expressed with a combination of
	descriptive assertions and RFC 2119 terminology. The key words “MUST”,
	“MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”,
	“RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this
	document are to be interpreted as described in RFC 2119.
	However, for readability, these words do not appear in all uppercase
	letters in this specification. </p>
  <p>All of the text of this specification is normative except sections
	explicitly marked as non-normative, examples, and notes. <a data-link-type="biblio" href="#biblio-rfc2119">[RFC2119]</a> </p>
  <p>Examples in this specification are introduced with the words “for example”
	or are set apart from the normative text with <code>class="example"</code>,
	like this: </p>
  <div class="example" id="example-ae2b6bc0">
   <a class="self-link" href="#example-ae2b6bc0"></a> 
   <p>This is an example of an informative example. </p>
  </div>
  <p>Informative notes begin with the word “Note” and are set apart from the
	normative text with <code>class="note"</code>, like this: </p>
  <p class="note" role="note">Note, this is an informative note. </p>
  <p>Advisements are normative sections styled to evoke special attention and are
	set apart from other normative text with <code>&lt;strong class="advisement"></code>, like
	this: <strong class="advisement"> UAs MUST provide an accessible alternative. </strong> </p>
  <h3 class="heading settled" id="conform-classes"><span class="content"> Conformance classes</span><a class="self-link" href="#conform-classes"></a></h3>
  <p>Conformance to this specification
	is defined for three conformance classes: </p>
  <dl>
   <dt>style sheet 
   <dd>A <a href="http://www.w3.org/TR/CSS2/conform.html#style-sheet">CSS
			style sheet</a>. 
   <dt>renderer 
   <dd>A <a href="http://www.w3.org/TR/CSS2/conform.html#user-agent">UA</a> that interprets the semantics of a style sheet and renders
			documents that use them. 
   <dt>authoring tool 
   <dd>A <a href="http://www.w3.org/TR/CSS2/conform.html#user-agent">UA</a> that writes a style sheet. 
  </dl>
  <p>A style sheet is conformant to this specification
	if all of its statements that use syntax defined in this module are valid
	according to the generic CSS grammar and the individual grammars of each
	feature defined in this module. </p>
  <p>A renderer is conformant to this specification
	if, in addition to interpreting the style sheet as defined by the
	appropriate specifications, it supports all the features defined
	by this specification by parsing them correctly
	and rendering the document accordingly. However, the inability of a
	UA to correctly render a document due to limitations of the device
	does not make the UA non-conformant. (For example, a UA is not
	required to render color on a monochrome monitor.) </p>
  <p>An authoring tool is conformant to this specification
	if it writes style sheets that are syntactically correct according to the
	generic CSS grammar and the individual grammars of each feature in
	this module, and meet all other conformance requirements of style sheets
	as described in this module. </p>
  <h3 class="heading settled" id="conform-responsible"><span class="content"> Requirements for Responsible Implementation of CSS</span><a class="self-link" href="#conform-responsible"></a></h3>
  <p>The following sections define several conformance requirements
		for implementing CSS responsibly,
		in a way that promotes interoperability in the present and future. </p>
  <h4 class="heading settled" id="conform-partial"><span class="content"> Partial Implementations</span><a class="self-link" href="#conform-partial"></a></h4>
  <p>So that authors can exploit the forward-compatible parsing rules to assign fallback values, <strong>CSS renderers <em>must</em> treat as invalid
		(and <a href="http://www.w3.org/TR/CSS2/conform.html#ignore">ignore as appropriate</a>)
		any at-rules, properties, property values, keywords, and other syntactic constructs
		for which they have no usable level of support</strong>.
		In particular, user agents <em>must not</em> selectively ignore
		unsupported property values and honor supported values in a single multi-value property declaration:
		if any value is considered invalid (as unsupported values must be),
		CSS requires that the entire declaration be ignored. </p>
  <h4 class="heading settled" id="conform-future-proofing"><span class="content"> Implementations of Unstable and Proprietary Features</span><a class="self-link" href="#conform-future-proofing"></a></h4>
  <p>To avoid clashes with future stable CSS features,
		the CSSWG recommends <a href="http://www.w3.org/TR/CSS/#future-proofing">following best practices</a> for the implementation of <a href="http://www.w3.org/TR/CSS/#unstable">unstable</a> features and <a href="http://www.w3.org/TR/CSS/#proprietary-extension">proprietary extensions</a> to CSS. </p>
  <h4 class="heading settled" id="conform-testing"><span class="content"> Implementations of CR-level Features</span><a class="self-link" href="#conform-testing"></a></h4>
  <p>Once a specification reaches the Candidate Recommendation stage,
		implementers should release an <a data-link-type="dfn" href="http://www.w3.org/TR/CSS/#vendor-prefix">unprefixed</a> implementation
		of any CR-level feature they can demonstrate
		to be correctly implemented according to spec,
		and should avoid exposing a prefixed variant of that feature. </p>
  <p>To establish and maintain the interoperability of CSS across
		implementations, the CSS Working Group requests that non-experimental
		CSS renderers submit an implementation report (and, if necessary, the
		testcases used for that implementation report) to the W3C before
		releasing an unprefixed implementation of any CSS features. Testcases
		submitted to W3C are subject to review and correction by the CSS
		Working Group. </p>
  <p>
   Further information on submitting testcases and implementation reports
		can be found from on the CSS Working Group’s website at <a href="http://www.w3.org/Style/CSS/Test/">http://www.w3.org/Style/CSS/Test/</a>.
		Questions should be directed to the <a href="http://lists.w3.org/Archives/Public/public-css-testsuite">public-css-testsuite@w3.org</a> mailing list. 
<script src="https://www.w3.org/scripts/TR/2016/fixup.js"></script>
  </p>
  <h2 class="no-num no-ref heading settled" id="index"><span class="content">Index</span><a class="self-link" href="#index"></a></h2>
  <h3 class="no-num no-ref heading settled" id="index-defined-here"><span class="content">Terms defined by this specification</span><a class="self-link" href="#index-defined-here"></a></h3>
  <ul class="index">
   <li>
    bar
    <ul>
     <li><a href="#dom-foo-bar">attribute for Foo</a><span>, in §2.1</span>
     <li><a href="#dom-foodict-bar">dict-member for FooDict</a><span>, in §2.1</span>
    </ul>
   <li><a href="#dom-foodict-baz">baz</a><span>, in §2.1</span>
   <li><a href="#dom-foo-baz">baz(Arg1, Arg2)</a><span>, in §2.1</span>
   <li><a href="#cross-references">Cross-references</a><span>, in §2.1</span>
   <li><a href="#descdef-some-at-rule-descriptor-foo">descriptor-foo</a><span>, in §2.2</span>
   <li><a href="#foo">Foo</a><span>, in §2.1</span>
   <li><a href="#propdef-foo">foo</a><span>, in §2.1</span>
   <li><a href="#dictdef-foodict">FooDict</a><span>, in §2.1</span>
   <li><a href="#dom-foodict-foos">foos</a><span>, in §2.1</span>
   <li><a href="#dfn-index">index</a><span>, in §2</span>
   <li><a href="#propdef-shorthand-foo">shorthand-foo</a><span>, in §2.2</span>
   <li><a href="#simplest">simplest</a><span>, in §2</span>
   <li><a href="#terms">terms</a><span>, in §2</span>
   <li><a href="#valdef-foo-value-name">value-name</a><span>, in §2.1</span>
   <li><a href="#variant">variant</a><span>, in §2</span>
  </ul>
  <aside class="dfn-panel" data-for="term-for-comb-one">
   <a href="https://drafts.csswg.org/css-values-4/#comb-one">https://drafts.csswg.org/css-values-4/#comb-one</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-comb-one">2.1. Internal display model: the foo property</a> <a href="#ref-for-comb-one①">(2)</a> <a href="#ref-for-comb-one②">(3)</a> <a href="#ref-for-comb-one③">(4)</a>
    <li><a href="#ref-for-comb-one④">2.2. Shorthands and Descriptors</a> <a href="#ref-for-comb-one⑤">(2)</a> <a href="#ref-for-comb-one⑥">(3)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-cssomstring">
   <a href="https://drafts.csswg.org/cssom-1/#cssomstring">https://drafts.csswg.org/cssom-1/#cssomstring</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-cssomstring">2.1. Internal display model: the foo property</a> <a href="#ref-for-cssomstring①">(2)</a> <a href="#ref-for-cssomstring②">(3)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-the-details-element">
   <a href="https://html.spec.whatwg.org/multipage/interactive-elements.html#the-details-element">https://html.spec.whatwg.org/multipage/interactive-elements.html#the-details-element</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-the-details-element">2. Sample section</a> <a href="#ref-for-the-details-element①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-the-dfn-element">
   <a href="https://html.spec.whatwg.org/multipage/text-level-semantics.html#the-dfn-element">https://html.spec.whatwg.org/multipage/text-level-semantics.html#the-dfn-element</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-the-dfn-element">2. Sample section</a>
    <li><a href="#ref-for-the-dfn-element①">2.1. Internal display model: the foo property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-the-div-element">
   <a href="https://html.spec.whatwg.org/multipage/grouping-content.html#the-div-element">https://html.spec.whatwg.org/multipage/grouping-content.html#the-div-element</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-the-div-element">2. Sample section</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-the-dl-element">
   <a href="https://html.spec.whatwg.org/multipage/grouping-content.html#the-dl-element">https://html.spec.whatwg.org/multipage/grouping-content.html#the-dl-element</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-the-dl-element">2.1. Internal display model: the foo property</a> <a href="#ref-for-the-dl-element①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-idl-boolean">
   <a href="https://heycam.github.io/webidl/#idl-boolean">https://heycam.github.io/webidl/#idl-boolean</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-idl-boolean">2.1. Internal display model: the foo property</a> <a href="#ref-for-idl-boolean①">(2)</a>
   </ul>
  </aside>
  <h3 class="no-num no-ref heading settled" id="index-defined-elsewhere"><span class="content">Terms defined by reference</span><a class="self-link" href="#index-defined-elsewhere"></a></h3>
  <ul class="index">
   <li>
    <a data-link-type="biblio">[css-values-4]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-comb-one" style="color:initial">|</span>
    </ul>
   <li>
    <a data-link-type="biblio">[cssom-1]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-cssomstring" style="color:initial">CSSOMString</span>
    </ul>
   <li>
    <a data-link-type="biblio">[HTML]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-the-details-element" style="color:initial">details</span>
     <li><span class="dfn-paneled" id="term-for-the-dfn-element" style="color:initial">dfn</span>
     <li><span class="dfn-paneled" id="term-for-the-div-element" style="color:initial">div</span>
     <li><span class="dfn-paneled" id="term-for-the-dl-element" style="color:initial">dl</span>
    </ul>
   <li>
    <a data-link-type="biblio">[WebIDL]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-idl-boolean" style="color:initial">boolean</span>
    </ul>
  </ul>
  <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
  <h3 class="no-num no-ref heading settled" id="normative"><span class="content">Normative References</span><a class="self-link" href="#normative"></a></h3>
  <dl>
   <dt id="biblio-css-syntax-3">[CSS-SYNTAX-3]
   <dd>Tab Atkins Jr.; Simon Sapin. <a href="https://www.w3.org/TR/css-syntax-3/">CSS Syntax Module Level 3</a>. 20 February 2014. CR. URL: <a href="https://www.w3.org/TR/css-syntax-3/">https://www.w3.org/TR/css-syntax-3/</a>
   <dt id="biblio-css-values-4">[CSS-VALUES-4]
   <dd>Tab Atkins Jr.; Elika Etemad. <a href="https://www.w3.org/TR/css-values-4/">CSS Values and Units Module Level 4</a>. 31 January 2019. WD. URL: <a href="https://www.w3.org/TR/css-values-4/">https://www.w3.org/TR/css-values-4/</a>
   <dt id="biblio-cssom-1">[CSSOM-1]
   <dd>Simon Pieters; Glenn Adams. <a href="https://www.w3.org/TR/cssom-1/">CSS Object Model (CSSOM)</a>. 17 March 2016. WD. URL: <a href="https://www.w3.org/TR/cssom-1/">https://www.w3.org/TR/cssom-1/</a>
   <dt id="biblio-html">[HTML]
   <dd>Anne van Kesteren; et al. <a href="https://html.spec.whatwg.org/multipage/">HTML Standard</a>. Living Standard. URL: <a href="https://html.spec.whatwg.org/multipage/">https://html.spec.whatwg.org/multipage/</a>
   <dt id="biblio-rfc2119">[RFC2119]
   <dd>S. Bradner. <a href="https://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>. March 1997. Best Current Practice. URL: <a href="https://tools.ietf.org/html/rfc2119">https://tools.ietf.org/html/rfc2119</a>
   <dt id="biblio-webidl">[WebIDL]
   <dd>Boris Zbarsky. <a href="https://heycam.github.io/webidl/">Web IDL</a>. 15 December 2016. ED. URL: <a href="https://heycam.github.io/webidl/">https://heycam.github.io/webidl/</a>
  </dl>
  <h2 class="no-num no-ref heading settled" id="property-index"><span class="content">Property Index</span><a class="self-link" href="#property-index"></a></h2>
  <div class="big-element-wrapper">
   <table class="index">
    <thead>
     <tr>
      <th scope="col">Name
      <th scope="col">Value
      <th scope="col">Initial
      <th scope="col">Applies to
      <th scope="col">Inh.
      <th scope="col">%ages
      <th scope="col">Ani­mat­able
      <th scope="col">Anim­ation type
      <th scope="col">Canonical order
      <th scope="col">Com­puted value
    <tbody>
     <tr>
      <th scope="row"><a class="css" data-link-type="property" href="#propdef-foo" id="ref-for-propdef-foo⑥">foo</a>
      <td>inline-inside | block-inside | table | ruby | icon
      <td>text
      <td>all elements
      <td>no
      <td>n/a
      <td>no
      <td>
      <td>per grammar
      <td>specified value
     <tr>
      <th scope="row"><a class="css" data-link-type="property" href="#propdef-shorthand-foo" id="ref-for-propdef-shorthand-foo">shorthand-foo</a>
      <td>foo | bar | baz
      <td>see individual properties
      <td>see individual properties
      <td>see individual properties
      <td>see individual properties
      <td>
      <td>see individual properties
      <td>per grammar
      <td>see individual properties
   </table>
  </div>
  <h3 class="no-num no-ref heading settled" id="some-at-rule-descriptor-table"><span class="content"><a class="css" data-link-type="at-rule">@some-at-rule</a> Descriptors</span><a class="self-link" href="#some-at-rule-descriptor-table"></a></h3>
  <div class="big-element-wrapper">
   <table class="index">
    <thead>
     <tr>
      <th scope="col">Name
      <th scope="col">Value
      <th scope="col">Initial
    <tbody>
     <tr>
      <th scope="row"><a class="css" data-link-type="descriptor" href="#descdef-some-at-rule-descriptor-foo" id="ref-for-descdef-some-at-rule-descriptor-foo">descriptor-foo</a>
      <td>more | values
      <td>values
   </table>
  </div>
  <h2 class="no-num no-ref heading settled" id="idl-index"><span class="content">IDL Index</span><a class="self-link" href="#idl-index"></a></h2>
<pre class="idl highlight def">/* Write WebIDL in a &lt;pre class="idl"> as plain text. */
<c- b>interface</c-> <a href="#foo"><code><c- g>Foo</c-></code></a> {
  <c- b>readonly</c-> <c- b>attribute</c-> <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring" id="ref-for-cssomstring③"><c- n>CSSOMString</c-></a> <a data-readonly data-type="CSSOMString" href="#dom-foo-bar"><code><c- g>bar</c-></code></a>;
  <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-boolean" id="ref-for-idl-boolean②"><c- b>boolean</c-></a> <a href="#dom-foo-baz"><code><c- g>baz</c-></code></a>(<a class="n" data-link-type="idl-name" href="#dictdef-foodict" id="ref-for-dictdef-foodict①"><c- n>FooDict</c-></a> <a href="#dom-foo-baz-arg1-arg2-arg1"><code><c- g>Arg1</c-></code></a>, (<a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring" id="ref-for-cssomstring①①"><c- n>CSSOMString</c-></a> <c- b>or</c-> <a class="n" data-link-type="idl-name" href="#foo" id="ref-for-foo①①"><c- n>Foo</c-></a>) <a href="#dom-foo-baz-arg1-arg2-arg2"><code><c- g>Arg2</c-></code></a>);
};

<c- b>dictionary</c-> <a href="#dictdef-foodict"><code><c- g>FooDict</c-></code></a> {
  <c- b>sequence</c->&lt;<a class="n" data-link-type="idl-name" href="#foo" id="ref-for-foo②①"><c- n>Foo</c-></a>> <a data-type="sequence<Foo> " href="#dom-foodict-foos"><code><c- g>foos</c-></code></a>;
  <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-boolean" id="ref-for-idl-boolean①①"><c- b>boolean</c-></a> <a data-type="boolean " href="#dom-foodict-bar"><code><c- g>bar</c-></code></a>;
  <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring" id="ref-for-cssomstring②①"><c- n>CSSOMString</c-></a> <a data-default="&quot;qux&quot;" data-type="CSSOMString " href="#dom-foodict-baz"><code><c- g>baz</c-></code></a> = "qux";
};

</pre>
  <h2 class="no-num no-ref heading settled" id="issues-index"><span class="content">Issues Index</span><a class="self-link" href="#issues-index"></a></h2>
  <div style="counter-reset:issue">
   <div class="issue"> An open issue or editorial remark is OK in a WD,
	but they should be resolved/removed before the document goes to “CR”
	(Candidate Recommendation).
	Use <code class="lang-html highlight">class="issue"</code> on an element,
	or begin a paragraph with “Issue:”.<a href="#issue-7d79807a"> ↵ </a></div>
   <div class="issue"> Inline issues will be copied into an <a href="#issues-index">Issues Index</a> at the end of the document,
	for easy reference.<a href="#issue-33d58da0"> ↵ </a></div>
   <div class="issue"> Make some considerations about privacy and security.<a href="#issue-2202014f"> ↵ </a></div>
  </div>
  <aside class="dfn-panel" data-for="propdef-foo">
   <b><a href="#propdef-foo">#propdef-foo</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-foo①">1. Introduction</a>
    <li><a href="#ref-for-propdef-foo②">2. Sample section</a> <a href="#ref-for-propdef-foo③">(2)</a>
    <li><a href="#ref-for-propdef-foo④">2.1. Internal display model: the foo property</a>
    <li><a href="#ref-for-propdef-foo⑤">2.2. Shorthands and Descriptors</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="cross-references">
   <b><a href="#cross-references">#cross-references</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-cross-references">2.1. Internal display model: the foo property</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="foo">
   <b><a href="#foo">#foo</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-foo">2.1. Internal display model: the foo property</a> <a href="#ref-for-foo①">(2)</a> <a href="#ref-for-foo②">(3)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="dictdef-foodict">
   <b><a href="#dictdef-foodict">#dictdef-foodict</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-dictdef-foodict">2.1. Internal display model: the foo property</a>
   </ul>
  </aside>
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